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Enzymes act on the APP (Amyloid precursor protein) and cut it into fragments of protein, one of which is called beta-amyloid and its crucial in the formation of senile plaques in Alzheimer (Photo credit: Wikipedia)

This morning, announced that its immunoglobulin(IG), a purified collection of antibodies from human plasma, failed to reduce cognitive decline and preserve functional abilities in patients with Alzheimer's disease. (See Bruce Japsen's piece here.)

As Baxter explains in this backgrounder, there was evidence that IG prevented the formation of plaques in the brains of Alzheimer's disease, probably by blocking a protein called amyloid beta. Although the idea is still hotly contested, most researchers believe that beta amyloid is a key factor in Alzheimer's disease.

Baxter had conducted studies that seemed to show IG might help patients, but the failure is not a surprise. Baxter stock is only down 3.6%, indicating this disappointment is not a real concern to investors. That's because other Alzheimer's drugs that targeted beta amyloid, including one from , , and Pharmaceutical and another from Eli Lilly, have failed.

Here's what may make scientists working on Alzheimer's disease nervous, though. Eli Lilly had noted a reason for hope when its Alzheimer's antibody failed: it seemed to work in patients with mild Alzheimer's disease, and not in those who had the more severe moderate form of the disease. Lilly is continuing to develop its drug. It would be comforting if the Baxter trial had found the same thing. That would mean that this approach was consistently working in the same group of patients Instead, Baxter says it is seeing efficacy in the moderate form of the disease. This is more in line with what you'd expect if targeting beta amyloid resulted in only slight benefits or none at all. There will probably be more information as Baxter scientists continue to look at the results.

The beta amyloid hypothesis will have plenty of opportunity to prove itself. It's possible that pills that work on the amyloid pathway, being developed separately by and Eli Lilly, will work better because they can get into the brain where antibodies can't. But a first read of today's results certainly seems to give amyloid doubters a little more ammunition.